This invention relates generally to ink jet printers and more particularly to drop detection arrangements for increasing the rate at which ink jet printhead nozzles are examined.
It is generally known to use drop detection devices to examine the operational status of printhead nozzles in ink jet printers. Some ink jet printers have a plurality of printheads. Drop detection devices are used to test the operational status of ink-ejection nozzles of a printhead. Depending on the test results, corrective measures may be implemented for proper operation.
Generally, drop detection devices are used to detect ink drops ejected by printhead nozzles. Based on the detection of ink drops, the status of a particular nozzle may be diagnosed. Typically, a printhead ejects ink drops in response to drive signals generated by print control circuitry in a printer. A printhead that ejects ink drops in response to drive signals may be referred to as a drop on demand printhead. Typically, there are two commonly used drop on demand technologies. These technologies are thermal (or bubble-jet) inkjet printing and piezo-electric (or impulse) inkjet printing. In thermal inkjet printing, the energy for ink drop ejection is generated by resistor elements, which are electrically heated. Such elements heat rapidly in response to electrical signals controlled by a microprocessor and creates a vapor bubble that expels ink through one or more nozzles associated with the resistor elements. In piezo-electric inkjet printing, ink drops are ejected in response to the vibrations of a piezo-electric crystal. The piezo-electric crystal responds to an electrical signal controlled by a microprocessor.
Nozzles through which ink drops are ejected may become clogged with paper fibers or other debris during normal operation. The nozzles may also become clogged with dry ink during prolonged idle periods. Generally, printhead service stations are used for wiping the printhead and applying suction to the printhead to clear out any blocked nozzles. The ink drop detectors may be used to determine whether a printhead actually requires cleaning. Additionally the detectors may be used to detect permanent failures of individual nozzles that may be caused, for example, by the failure of heating elements (in thermal ink jets) or by the failure in the piezo-electric crystals (in impulse printers). Drop detection devices may also be used to calibrate the nozzle position relative to other parts of the printing machine.
Well known drop detectors include optical drop detection circuits. Optical drop detection circuits typically include a light sensor such as a photodiode that senses the light provided by a light source such as a light emitting diode (LED). When a drop is present in the light path between the light sensor and the light source, the output of the light sensor changes because the amount of light sensed by the light sensor is reduced by the presence of the ink drop. The output of the light sensor is typically amplified and analyzed to determine whether an ink drop passed through the path between the light source and the light sensor.
It is generally well known to include optical drop detection devices in inkjet printers. For example, the DESIGNJET(trademark) 1050 and the DESIGNJET(trademark) 5000 both include optical drop detection technology. As used in the DESIGNJET(trademark) 1050 and the DESIGNJET(trademark) 5000, the drop detector is placed in the printer next to the service station. When drop detection is to be done, the carriage moves to position the printhead over the drop detection device. When the first printhead has finished the drop detection process, the carriage moves to position the second printhead over the drop detection device. The same process is repeated for all the printheads. With respect to the process for each printhead, a first nozzle to be detected is fired. The drop detection device detects drops from the first nozzle. Then a second nozzle to be detected is fired. This process is repeated with all the nozzles on the particular printhead.
There are several disadvantages associated with existing drop detection methods. One of which is that only one nozzle can be detected at the same time. This is especially pertinent considering that the number of printheads and nozzles per printer has increased throughout the years. Furthermore, future printheads may have up to sixteen times more nozzles than present, and the present arrangements in which only one nozzle is evaluated at a time may adversely affect the efficiency of printing processes. Therefore, present methods of drop detection can be categorized as low throughput methods.
In one respect, the invention is a method for ascertaining the operational status of printhead nozzles. The method includes the step of firing a plurality of the nozzles. In this respect, the plurality of nozzles are fired substantially simultaneously. The method for ascertaining the operational status of the printhead nozzles also includes the step of detecting the substantially simultaneously fired ink drops. The method further includes the step of determining the status of each of the plurality of printhead nozzles. Nozzle status is determined based on results from the detecting step.
In another respect, the invention is a drop detection arrangement for monitoring a plurality of printhead nozzles. The drop detection arrangement includes a printhead arrangement with at least one printhead. Each printhead has a plurality of nozzles. In this respect, the drop detection arrangement also includes a drop detector for detecting ink drops that are substantially simultaneously ejected from the plurality of nozzles. The drop detection arrangement also includes a microprocessor. The microprocessor is configured to determine the nozzle status of each of the plurality of nozzles based on the detected ink drops.
In yet another respect, the invention is a method for testing the nozzles of a printhead arrangement. In this respect, the method includes choosing a group of nozzles to be fired. The method also includes selecting a group of nozzles to be fired and firing the selected nozzles substantially simultaneously. In this respect the method also includes the step of detecting the substantially simultaneously fired ink drops. The method also includes the step of determining the status of each of the selected nozzles based on the detection of the ink drops.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain aspects, including some or all of the following: performing high throughput drop detection; and increased print quality and product reliability. Those skilled in the art will appreciate these aspects of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.